On Mon, 8 Feb 2010, Felix Buenemann wrote:
I was under the impression, that using HW RAID10 would save me 50% PCI bandwidth and allow the controller to more intelligently handle its cache, so I sticked with it. But I should run some benchmarks in RAID10 vs. JBOD with ZFS mirrors to see if this makes a difference.
The answer to this is "it depends". If the PCI-E and controller have enough bandwidth capacity, then the write bottleneck will be the disk itself. If there is insufficient controller bandwidth capacity, then the controller becomes the bottleneck. If the bottleneck is the disks, then there is hardly any write penalty from using zfs mirrors. If the bottleneck is the controller, then you may see 1/2 the write performance due to using zfs mirrors.
If you are using modern computing hardware, then the disks should be the bottleneck.
Performance of HW RAID controllers is a complete unknown and they tend to modify the data so that it depends on the specific controller, which really sucks if the controller fails. It is usually better to run the controller in a JBOD mode (taking advantage of its write cache, if available) and use zfs mirrors.
Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
